1. Field
The invention is in the field of information storage media, such as magnetic tape or compact laser discs upon which information is stored and may be read back from the media by means of a machine.
2. State of the Art
It is currently common practice to record information, such as sound information, on magnetic tape or discs of various types to be played back from the media through use of a machine, such as an audio tape player or a compact disc player. For example, it is common to supply music or spoken words on magnetic tape in a cassette device for playback by the purchaser of the tape cassette in an audio tape player. When the information is recorded onto the tape, it is placed thereon so that it can be played back or read intelligibly by the machine at a preset constant speed. If played back or read at a speed substantially different from the preset speed, the information becomes unintelligible or unpleasant. Thus, normal prerecorded music cassettes are recorded so that they should be played back at a standard tape speed of 4.8 centimeters per second. Most cassette playback equipment commercially available is designed to play back cassette tapes at this standard speed. In this way substantially all prerecorded cassette tapes and cassette tape playback equipment are compatible so that such tapes may be played back on any standard cassette playback machine.
The size of the standard cassette limits the amount of tape that can be held in the cassette. The amount of tape in the cassette, in turn, limits the amount of material that can be recorded on the tape. The speed at which the tape is designed to be played back determines the amount of information that can be stored on a given length of tape. Thus, the slower the speed at which the tape is designed to be played back, the greater the information that can be stored on the tape.
However, the currently known systems for reading information that is stored on magnetic tape are speed dependent. The speed at which a tape passes the head in a tape playback machine which reads the information stored on the tape has a significant effect on the frequency response obtainable for the played back information. The frequency response is important because it affects the fidelity of the played back information. The standard cassette speed was chosen to give staisfactory high frequency response for the played back signals with state of the art tape and magnetic playback heads while at the same time, going as slowly as possible to give maximum information storage on the tape. Any reduction in tape speed reduces the frequency response. Similarly, with compact discs, it is the number of bits of digital information provided for any given playback time unit that determines the frequency response.
While high frequency response giving high fidelity sound reproduction is generally considered a necessity for music reproduction, reproduction of the spoken word does not require such high fidelity so does not require such high frequency response. Over the past several years, cassette record and playback equipment has been developed which operates at speeds below the standard speed. For example, Norwood Industries, Inc., Salt Lake City, Utah, has developed and markets several cassette record and playback machines which operate at one-quarter normal speed. This reduction in speed allows four times as much information to be recorded on a given length of tape so that a cassette which can normally hold ninety minutes of information at standard speed, will contain six hours of information at one-quarter standard speed. These machines also operate as monaural machines so that information can be recorded on each of the normal four track of a cassette tape and played back separately rather than having the two separate stereo signals recorded on two of the tracks and played back simultaneously. This separate playback of each track of information doubles again the amount of playback time obtainable from a standard cassette so that twelve hours of monaural information can be obtained from a standard ninety minute cassette. This increase in recorded or stored information allows readings or dramatizations of entire novels or other books to be stored on a single cassette tape.
Prerecorded cassette or other tapes, or other media upon which such information may be stored, are supplied to be played at a single preset speed. Thus, most cassette tapes are recorded to be played back at normal speed, with a number of tapes now available to be played back at one-quarter speed. However, tapes are not supplied with some information recorded to be played back at one speed and other information to be played back at another speed.